DESCRIPTION: We will adapt fragment-complementation technology, originally developed for the investigation of protein-protein interactions, to engineer a new type of selectable marker and so facilitate selection of transformed, green plants expressing multi-subunit therapeutic proteins. With the Split Selectable Marker (SSM), which we propose to develop with the npt II gene (encoding neomycin phosphotransferase), the creation of these transgenic plants will occur more quickly, with less effort and will enhance their strategy for producing low-cost monoclonal antibodies for human and animal health. The SSM may also be disabled to yield transgenics with no functional selectable marker. Secretory immunoglobulin A (SIgA) has demonstrated pH and proteolytic stability in the mucosal environment and is tetravalent, making it the preferred antibody for passive immunotherapy. The engineering of crops for the production of antibodies represents the most inexpensive way of making large amounts of monoclonal SIgA. PROPOSED COMMERCIAL APPLICATION: The utility of the Split Selectable Market will be demonstrated during the production of the mononclonal plantibody called DoxoRx. This plantibody binds doxorubicin, as well as structurally related anthracycline-based chemotherapeutic agents. Individuals undergoing chemotherapy with these compounds often suffer hair loss and we plan to develop DoxoRx into a topically applied product to prevent this form of alopecia. When administered orally, DoxoRx may also combat mucositis, which is another side effect of anthracycline- based regimens of chemotherapy.